Indian Journal of Chemical Technology VoLI,July 1994,pp. 237-240

Mercury in Indian coals

S B Ghosh, M C Das, B Ghosh, R R P Roy & N N Banerjee Central Fuel Research Institute, 828 108,

Mercury in Indian coals belonging to different geological period and in some fly ash and bottom ash samples obtained from thermal power stations has been determined. A wide range of variations in mercury content from the value as low as 0.01 to as high as 1.5 ppm in coal samples have been observed. The fly ash and bottom ash samples mostly contain less than 0.005 ppm of mercury. The concentrations of mercury in different specific gravity fractions of four coal samples show that the metal is concentrated mostly in the fractions 1.6-1.7 and asbove 1.7 indicates its inorganic associa- tion in the fossil fuel.

Mercury is known to have practically no benefi- Experimental Procedure cial effect on human body and is highly toxic ex- In order to .retain mercury in the samples and hibiting a special propensity for cellulex deposi- to avoid volatilisation losses of mercury during LT tion and retention disrupting the function of cen- ashing procedure, dissolution of coal and lignite tral nervous system and other organs of human samples was done in oxygen bomb calorimeter in body. Its study is of paramount importance from presence of 5% HN03 solution. The method for the point of view of its dissipative nature causing bottom ash and fly ash sample preparation was environmental hazards from burning huge quantit- followed as reported earlier", ies of coal and lignites in thermal power stations. A Philips PU-9360 continuous hydride vapour Air is contaminated through the emission of mer- generation system linked with a Pye Unicam cury vapours, and dust containing mercury. The SP2900 atomic absorption spectrophotometer, emission and distribution of this metal is different was used for mercury estimation. Sodium borohy- from other trace metals due to its low melting and dride was used as reducing agent in all cases as it boiling point with monoatomic nature in vapour was found more effective in terms of speed and phase. This enhances its fallout in the nearby area efficiency of reduction of the metal in the sample of the power plant from its subsequent emission solution. Concentration of mercury was deter- from the stack. The deposited mercury at the vi- mined from the calibration curve drawn for the cinity of power plant leads to rapid vaporisation metal in appropriate ranges. due to its volatile nature. The rate of vaporisa- tion also depends on the local condition of the Results and Discussion fallout site. The effluent water may contain mer- Results for mercury in coals belonging to differ- cury in various forms. The toxic severity becomes ent geological period alongwith their origin and more when mercury is converted by bacteria in ash content are given in Table 1. It is apparent the muddy sediment into organic mercurials The from the samples analysed in the present study fish and other aquatic forms of life grown in such (Table 1) that the lignites are covered by the contaminated water, in turn, affect human beings range 0.01-0.21 ppm mercury, mean value 0.06 when they eat them CiS a food 1.2. (as ppm mercury). Tertiary coals from Assam by Mercury content in foreign coals are well docu- 0.02-0.30 ppm (mean value 0.16), coals from mented. However, information on Indian coals Jammu & Kashmir by 0.72-0.87 ppm (mean value are not available. Mercury was found in some 0.80), coals from Damodar Valley coalfields by Russian coals ' in quite high concentrations of up 0.01-1.0 ppm, (mean value 0.52) and the coals to 20 ppm. It is reported in the range of U.Ol- from Son Mahanadi coalfields are covered by the 0.40 ppm in Australian coals">. Belgean coals" range 0.10-1.10 ppm with mean value of 0.56 contain mercury in the range 0.2-2.0 ppm. Cana- ppm mercury. dian coals 7 have been found to contain mercury The largest user of coal and lignite in India is in the range less than 0.03-1.3 ppm. Extensive the power sector consuming about fifty per cent studies on mercury in American coals (0.01-2.0 of the present production. The coals from Damo- ppm) have been reported", dar Valley coalfield (S1. Nos. 16-20 and 22-31) 238 INDIAN J. CHEM. TECHNOL., JULY 1994

Table I-Mercury content of some Indian coals and lignites Table 2-Distribution of mercury in different specific gravity fractions of some coals and lignite Sample details Ash, Hg content in % wt ppm in coal Specific Float, % Ash,% Hg content of gravity bywt. wt coalinppm 1 Nicham Lignite, Kashmir 55.6 0.21 2 Palana lignite, Rajasthan 12.7 0.01 Kalakot coal <1.3 0.4 2.2 3 Kutch lignite, Gujarat 19.5 0.03 1.3-1.4 44.7 8.9 0.42 4 Mehsona lignite, Gujarat 7.2 0.02 1.4-1.5 32.9 16.1 0.61 5 Neyveli lignite, Tamil Nadu 3.2 0.03 1.5-1.6 9.4 20.5 0.65 6 Makum coal, Assam 4.1 0.50 1.6-1.7 0.9 25.4 1.14 7 Baragolai coal, Assam 10.1 0.06 >1.7 11.7 73.5 3.21 8 Baragolai coal, 20ft seam (OV), Overall 100 19.9 0.87 Assam 4.4 0.02 Metkacoal 9 Baragolai coal, 60ft seam IV, Assam 3.5 0.09 <1.3 5.2 3.4 0.95 10 Baragolai coal, 60ft seam V, Assam 4.0 0.02 1.3-1.4 43.0 3.8 1.02 11 Baragolai coal, 60ft seam VI, Assam 4.3 0.03 1.4-1.5 20.5 17.2 1.12 12 West Dharangiri coal, Assam 6.7 0.31 1.5-1.6 9.5 24.2 2.13 13 Talcher coal, Orissa 42.2 0.15 1.6-1.7 4.4 30.6 1.03 14 Metka coal, J&K 21.2 0.72 > 1.7 17.4 57.5 1.50 15 Kalakot coal, J&K 19.9 0.87 Overall 100 21.2 0.72 16 Bazna colly (OCP), Raniganj 17.5 0.49 Ta1cher coal 17 Lakhimata colly, Raniganj 24.8 0.04 <1.5 53.9 18.9 0.08 18 Nabakajora colly, Raniganj 35.9 0.39 1.5-1.6 7.2 35.9 0.12 19 Kapasara colly, Raniganj 30.9 0.80 1.6-1.7 16.0 43.1 0.05 20 North colly, Raniganj 42.4 9.80 1.7-1.8 4.9 53.7 0.32 21 Lalmatia colly, Rajmahal 37.0 0.55 > 1.8 18.0 71.0 0.63 !2 Chasnala colly, ~9.5 0.60 Overall 100 42.2 0.15 23 colly, Jharia 26.7 0.25 Nichham lignite 24 Nudkhurkee colly, Jharia 47.6 0.59 <1.4 0.1 25 Sudamdih colly, Jharia 21.2 0.09 1.4-1.5 1.5 19.6 0.05 26 colly 45.2 0.65 1.5-1.6 23.6 44.1 0.12 27 Dakra colly, Dakra 35.0 0'80 1.6-1.7 14.5 51.6 0.13 28 Central Sounda colly 32.5 0.75 >1.7 60.3 62.2 0.31 29 Kerketta colly 30.0 1.00 Overall 100 55.6 0.21 30 Karo Spl. East Bokaro 37.1 0.63 31 Dhori colly, East Bokaro 32.4 0.27 32 Jayant Mine, Tura Seam, Singrauli 25.7 0.10 cent ration and their use in thermal power stations 33 Purewa, Top Seam, Khadia Block, may cause contamination; or poisoning of soils, Singrauli 23.0 0.50 water and vegetations from its fallout. 34 Kotma Seam, Sohagpur 31.3 0.33 Mercury contents of different gravity fractions 35 Charcha colly, Sohagpur 14.0 0.89 of Kalakot and Metka coals from Jammu & 36 West Chirimiri colly, Chirimiri 12.5 0.38 Kashmir, Talcher coal from Orissa and one lignite 37 Upper Patphari Seam, Bhatgaon sample from Nicham, are given in Table 2. It is Mine, Bisrampur 30.7 0.62 observed from the table that mercury is mainly 38 Upper Kusmunda Block, Korba 33.8 0.50 associated with the inorganic fractions of the coal 39 Belphar Block, 1b river CF 22.1 1.10 mass. The study of coals from Iowa (USA)9 and 40 Patherdih washery (middlings). 35.2 0.27 Donet basin (USSR)IO suggested that mercury is 41 Dugdha washery (middlings) 34.8 0.52 mostly associated with pyrite in coal mass. Being a toxic element it is suggested that beneficiation and Sone-Mahanadi coalfield (Sl. Nos. 32-39) are of the coals should be carried out prior to their mostly used for power generation in major ther- uses in industries to reduce mercury contents II. mal power stations situated in the states of West By washing coals by different coal cleaning proce- Bengal, Bihar, Uttar Pradesh and Madhya Pra- dures mercury alongwith other toxic trace desh. The mean values, 0.52 and 0.56 ppm mer- metals'<':' especially those of environmental sig- cury respectively, may be considered a high con- nificance", could be removed but this in turn may GHOSH etal: MERCURY IN INDIAN COALS 239

Table 3-Mercury content in feed coal, fly ash and bottom ash samples from (a) Chandrapura, (b) Patratu, (c) Bokaro, (d) Ban- del, (e) Durgapur (DVC), (fJ Farakka, thermal power stations NameofTPS Sample Type Source Hg content in ppm (a) Chandrapura Feed coal Nudkharkee colly 0.22 Muraidih colly 0.65 Pipradih colly 2.00 Dhori Group 0.55 Dugda washery (middling) 0.52 Bottom ash Boiler, Unit I <0.005 Boiler, Unit II <0.005 Fly ash ESP, Unit I 0.01 Mechanical Separator Unit I 0.03 (b) Patratu Feed coal Kerketta colly 1.00 Dakracolly 0.80 Bottom ash Boiler Unit I <0.005 Boiler Unit II <0.005 Fly ash ESP, Unit I 0.008 (c) Bokaro Feed coal Dhori colly 0.27 Karo BpI. colly 0.63 Bottom ash Boiler, Unit I <0.005 Boiler, Unit II <0.005 Fly ash ESP, Unit I 0.007 (d) Bandel Feed coal Shankarpur colly 0.31 New Kendla colly 0.05 Washery middlings 0.85 Bottom ash Boiler 0.005 Fly ash ESP 0.006 (e) Durgapur (DVC) Feed coal Kapasara colly 0.80 Lakhimata colly 0.55 Bottom ash 0.08 Fly ash 0.005 (f)Farakka Feed coal Lalmatia colly 0.55 Chasnala washery (midd) 0.85 Bottom ash Boiler <0.005 Fly ash ESP 0.005

increase the concentration of these elements in the bottom ash samples may be attributed to the the rejects. Pyrites containing toxic trace elements presence of unburnt or partially burnt coal sam- under certain condition may be oxidised giving pies .. The combined effect of condensation of solutions of low pH which can solubilise some of mercury vapours on finer fly ash particles and in- these toxic metals including mercury and which in combustible ash from the boiler, are responsible turn may contaminate nearby lakes, ponds, soils, for larger mercury content in fly ash particles. etc. Table 3 shows the distribution of mercury The variations observed between bottom ash and contents in feed coal, bottom ash and fly ash sam- fly ash samples, and vapour phase samples have ples obtained from a few thermal power stations. been explained by Botton et al.15 as due to the It is observed that the partition of mercury in the combustion environment and the design of the bottom ash and fly ash samples are significantly plant. Newer and more efficient power plants are low and in most cases fly ash samples contain being designed where emission of volatile mercu- more mercury than bottom ash samples. Due to ry are reduced by increasing the adsorption rate the highly volatile nature of mercury, most of the of the metal on the suspended fly ash particles 16. metal escapes alongwith the flue gas through the Most of the mercury present in coal is emitted chimney into the atmosphere. Mercury content in in the form of vapour because mercury com- 240 INDIAN J. CHEM. TECHNOL., JULY 1994

Table 4-Mercury discharged in tonnes per annum from combustion of coal in TPS Name of thermal Total capacity, Coal consumed, Wt. average of Hg. Range of Hg AmountofHg power station MW tonne/day content in feed content, ppm likely to be thrown coal, ppm in the atmos tonne/annum Chandrapura 780 7,800 0.62 0.2-2.0 1.765 Patratu 840 8,400 0.85 0.5-1.5 2.606 Bokaro 240 2,400 0.45 0.2-0.85 0.394 Bandel 570 5,700 0.59 0.05-1.3 1.24 Durgapur (DVC) 474 4,740 0.71 0.7-1.2 1.23 Farakka (STPS) 2100 21,000 0.57 0.05-1.0 4.369

pounds are unstable at high temperature involved 5 Knott A C & Warbrooke P, Determination of trace ele- in coal combustion. Table 4 gives an idea of the ments in coal and coal products. Part-S Characterisation quantity of coal used per day and the amount of of a range of Australian raw coal. Rep. NERDDP No. EG 85/392 (1983) 55. mercury likely to be discharged in the atmosphere 6 Block C '& Dams R, Environ Sci Technol, 9 (1975) 146- per annum from some of the thermal power 150. stations as mentioned in Table 3. 7 Faurschou D K, Bonnell G W & Janke L C, Analysis di- rectory of Canadian Commercial Coals-Supplement No. 4, CAN MET Rep. No.- 82-13E(1982) 192. Conclusion 8 Zubovic P, Hatch J R & Medlin J H, Assessment of the It may be concluded that Indian coals are rela- Chemical Composition of Coal resources, UN Symp tively rich in mercury contents. They are mostly "''arid Coal Prospects Rep. No. TCD/NRETI AC. 12/EP/ associated as inorganic combination in the coal 15 (1979) 24. 9 Hatch J R, Avcin M J & Van Drope P E, Element Gelr mass. Utmost awareness should be taken to avoid chemistry of Cherookee group coals (middle Pennsylvani- mercury contamination from the various uses of an) from South-Central and South-Eastern Iowa, Iowa these coals, particularly, to the combustion in old Geol Surv Tech Pap No.5, (1984) 108. and inefficient power plants without adequate 10 Dvornikov A G, Dokl Akad Nauk USSR, 172 (1967) 211- 213. particulate control measures. It is also stressed 11 Schultz H, Hattman E A & Booher W B, Am Chern Sac that washery rejects being a potential source of Div Fuel Chern Prepr, 18(4)(1973) 108-113. mercury contamination, should be regularly moni- 12 Banerjee NN, Rao H S & Lahiri A, Indian J Technol, 12 tored for their mercury concentration before their (1974) 353-358. use or disposal. 13 Ghosh B, Biswas Dllip & Banerjee N N, Indian J Tech- nol, 17 (1979) 61-64. 14 Ghosh B, Das M C, Ghosh S B & Banerjee N N, Indian References J Technol, 24 (1987) 467-470. 1 Hamilton E I, Science Total Environ, 3 (1974) 3-85. 15 Botton N, Van Hook R, Fulkerson W, Lyon W & Andren 2 Dunlop L, Chern Eng News, 49 (1971) 22- 34. A, Trace Element measurements at the coal-fired Allen 3 Dvornikov A G, Dokl Acad Nauk SSSR, 172 (1967) 199- Steam Plant: Progress Report, June 1971-Jan. 1973, Ten- 202; Chern Abstr, 66, 57653. nessee, Oak Ridge National Library Supp. (Mar 1973), 4 Swaine D J, Godbeer W C & Morgan N C, Variations in Report No. OR NL-NSF-EP-43. contents of trace elements in coal from one seam Rep. 16 Kalb G W, in Trace elements in fuel edited by Babu S P, NERDDP, No. EG84/339 (1984) 103. Adv Chern Ser, Am Chem Soc, Washington, DC, 1975.